GaN Epitaxial Growth by Molecular Beam Epitaxy utilizing AlGaN Buffer Layer with Nanopipes

摘要

GaN layers were grown on AlGaN with nanopipes by molecular beam epitaxy (MBE) and analyzed. AlGaN films were grown by MBE using rf-plasma nitrogen source under metal-rich condition. Within the Al composition range of 0.5-0.6, open-end nanopipes were formed at the surface of AlGaN films with a density of ～6x10~9 cm~(-2) and a size ranging from 10 to 20 nm. These nanopipes, observed within ～300 nm of the surface, served as a nanoporous AlGaN template for re-growth of GaN epilayers. GaN epilayers grown to different thickness by MBE were studied for their microstructural and optical properties. For an AlGaN buffer layer with dislocation density of 3x10~(10) cm~(-2) near its surface, the overlaying GaN layers with thickness ranging from 0.1 μm to ～2μm were grown and analyzed by transmission electron microscopy for dislocation density. The GaN layer started with hexagonal islands on the nanopiped AlGaN and began to coalesce at about 0.1 μm thickness. At a thickness of 2.0 μm, the dislocation density reduced to ～ 1 x 10~9 cm~(-2) . Low temperature photoluminescence data demonstrate the improved optical quality of GaN epilayer grown on the porous AlGaN buffer layer.